Methods of introducing photo-curable groups into polymers, copolymer, and prepolymers are described in the prior art. See, e.g., U.S. Pat. Nos. 5,936,052; 5,508,317; and 2,837,512. In these methods, photo-curable moieties are often incorporated into polymeric materials by tethering acrylate, methacrylate or other types of vinyl groups to the polymers. Nucleophilic reactions involving moisture sensitive functional groups such as epoxy, isocyanate, anhydride, acylhalide or alkylhalide are often employed to attach photo-curable moieties to materials. These moisture sensitive groups serve as links for attaching the vinyl containing reagents to polymers. Either the polymer or the vinyl-functionalizing reagent can contain the nucleophilic groups. Likewise, either the polymer or the functionalizing group can contain the linking groups. However, the presence of moisture sensitive groups in either a polymer or reagent used for functionalizing the polymer limits or prevents the use of water in the reaction solvent.
U.S. Pat. No. 5,508,317 describes a method of introducing vinyl groups into PVA in an aqueous medium. The vinyl groups are attached to the PVA by allowing methacrylamidoacetaldehyde dimethylacetal to react with neighboring hydroxy groups in the PVA. The resulting acetal that links photo-curable groups to the polymer is a six membered ring. Ring forming reactions become kinetically unfavorable as ring size increases. Therefore, if hydroxy groups are spaced too far apart, then incorporation of vinyl groups through acetal formation will be difficult. Acetal formation is also constrained by the relative stereochemistry of hydroxy groups. For example, the relative stereochemistry of neighboring hydroxy groups in many poly(saccharides) is trans. Incorporation of vinyl groups into such materials through acetal chemistry is not favorable.
The acetal forming reactions in systems such as PVA cause the main polymer chain to become part of a ring. Fusing a ring to the main chain of a polymer is known to cause increases in glass transition temperature and decreases in the mobility or flexibility of the main chain. For applications requiring flexible polymer backbones, this is undesirable. Acetal formation can be the result of inter- or intra-molecular reaction of hydroxy groups. Intra-molecular reaction results in the formation of cyclic acetal. In polymeric systems, inter-molecular reactions result in cross-linking upon acetal formation.
Furthermore, many poly(saccharides) are insoluble or poorly soluble in organic solvents. For such systems, the invention disclosed here provides a practical method of introducing photo-curable groups into hydroxy- or amide-containing materials where the above methods would be impractical.